The invention relates to a module for filtration by reverse osmosis intended to be used in equipment filtering a liquid under pressure.
It is known in the field of reverse osmosis to use filter modules comprising foliar semi-permeable membranes wound as helices around a central mandrel. This mandrel is transversed by an axial duct allowing collection at the center of the module of the filtered permeate: the liquid to be filtered is taken in under pressure around the module and the central mandrel duct communicates axially with a low-pressure chamber receiving the filtered liquid. Such a module has the shape of a solid cylinder immersed in the liquid to be filtered. The use of foliar membranes and their helical arrangement make it possible to substantially reduce the bulk of the module for a given membrane surface.
However such a module cannot be used in some applications because it is by its very design a compact cylinder with its central part taken up by the mandrel collecting the filtered liquid. Illustratively, the object of U.S. Pat. No. 4,452,696 is an apparatus for producing fresh water and containing a reverse osmosis module of a generally annular shape of which the central part must be clear in order to pass a movable piston.
In this case as a rule membranes are used in the form of hollow fibers or braids wound around a tubular support. However this type of membrane is much bulkier for a given semi-permeable area.
The object of the present invention is to create a new reverse osmosis, pressurized filter module provided with foliar filter membranes wound in a spiral in order to benefit from a highly advantageous filtration/bulk ratio which providing an entirely clear central part for applications of the type cited above.
Another object is to simplify the module installation in the filtration equipment.